A typical laser scanning system is utilized in electronic prepress operations to write or record images for subsequent reproduction or to scan a prerecorded image at a predefined resolution rate. Such scanning systems may write or record images onto a recording media including photo or thermal sensitive paper or polymer films, photo or thermal sensitive coatings or erasable imaging materials mounted onto an image recording surface or photo or thermal sensitive paper, polymer film or aluminum base printing plate materials, all used in electronic image reproduction. Other scanning systems may read or scan an image recorded on a film negative, photographic paper or other substrate for digitizing the image. In each of these applications, different size media are used depending on the image to be scanned. Such media are mounted onto a support media surface which may be flat or curved (e.g., semi-cylindrical drum) and scanned with a recording or scanning beam.
The media may be held to the support surface by vacuum which is applied through vacuum ports disposed over the support surface. Typically, a constant vacuum pressure is applied drawing an equal volume of air through each of the vacuum ports disposed over the entire media support surface, regardless of the size of the media. Thus, larger size media are held more firmly to the support surface than smaller media because the larger media cover more vacuum ports thereby reducing leakage in the vacuum system allowing for greater vacuum. In order to reduce air loss in the vacuum system when not all the vacuum ports are covered by the media, it would be advantageous to apply vacuum to only those vacuum ports covered by the media. This will also allow smaller size media to be held more firmly to the support surface without increasing the vacuum capacity of the system.
It is known in the prior art to provide a series of grooves or groove patterns along the media support surface with each groove connected to one or more vacuum ports such that as air is drawn from a vacuum port the media is drawn onto the recording surface and air is further drawn from the groove thereby drawing the media down onto the media support surface over a wider area. A problem with these systems is that during the loading of the media onto the media support surface the media leading edge often catches in the grooves causing the media to buckle and jam. Ideally, groove patterns disposed in the support surface should not interfere with the travel of the media as it is loaded onto the support surface.
Finally, different thickness media (or media with different rigidity characteristics) are utilized in the scanning process. A problem arises if the vacuum applied causes the media to flex as it drawn into the groove pattern. Therefore, there remains a need to adjust the level of vacuum depending on the stiffness characteristics of the media.